1. Field of the Invention
The present invention relates to Bi-Pb-Sr-Ca-Cu-O system superconductors which have a zero resistance critical temperature (T.sub.c) of at least 107 K. or 108 K., in some cases, at least 110 K.
2. Description of the Related Art
In 1988, the researchers in the National Institute for Metals, Japan found a Bi-Sr-Ca-Cu-O system superconductor having T.sub.c of 105 K. which was obtained by extrapolation of the measured date. However, hitherto, it has been believed that it is very difficult to produce a Bi-Sr-Ca-Cu=O system superconductor which has T.sub.c of 105 K. or higher and contains a high T.sub.c phase in a large volume percentage with good reproducibility.
The present inventors synthesized a superconductor comprising a Bi-Sr-Ca-Cu-O system to which Pb is added and found that such new Bi-Pb-Sr-Ca-Cu-O system superconductor had T.sub.c of 107 K. However, it is still difficult to produce the Bi-Pb-Sr-Ca-Cu-O system superconductor having T.sub.c of 107 or higher and containing the high T.sub.c phase in a larger volume percentage with good reproducibility. Very few scientists have been able to synthesize such superconductor.
The Y-Ba-Cu-O system superconductor which was found in 1987, the Bi-Sr-Ca-Cu-O system superconductor and the Bi-Pb-Sr-Ca-Cu-O system superconductor have T.sub.c higher than the liquid nitrogen temperature, namely 77 K. and attract great attention worldwidely. But, it is still desired to provide a superconductor having higher T.sub.c since when difference between the liquid nitrogen temperature and T.sub.c is greater, the superconductor has better and more stable superconductive characteristics.